In recent years, electronic ballasts employing inverter technology have become popular for use as a discharge lamp lighting device for lighting a discharge lamp. Conventionally, built-in type ballasts (also referred to as OEM type ballasts) have been the primary form of commercial discharge lamp lighting device that have been produced. OEM type ballasts are defined as a discharge lamp lighting device that is delivered to a lighting fixture factory that incorporates the discharge lamp lighting device (ballast) into a lighting fixture produced in the factory, which then ships the finished product for sale.
In recent years, the demand for so-called “indoor type ballasts” (also referred to as or retrofit type ballasts) has increased. A retrofit type ballast comprises a discharge lamp lighting device that is delivered to a job site for connection to at least one light fixture that has previously been installed on the job site. The retrofit type ballast is typically placed near the light fixture, or may be wired into the fixture itself.
Retrofit type ballasts generally include an input terminal unit and an output terminal unit. The input terminal unit comprises, for example, a terminal block to which electrical leads are connected, or just electrical wires, that connect the ballast to a commercial power source that supplies AC electrical power. The output terminal unit comprises, for example, a terminal block to which electrical wires are connected, or just electrical wires, that connect the ballast to a lighting fixture (i.e., discharge lamp).
It is more likely that a wiring error will occur with respect to the installation of a retrofit ballast by an electrician or do-it-yourself installer, as compared to the installation of an OEM ballast by a fixture manufacturer, especially when the ballast is to be installed in a place having poor visibility for the installer, such as, but not limited to, for example, on a ceiling. For example, the installer may mistake the output terminals for the input terminals, and connect the commercial power supply to the output terminal and thereafter, turn ON the commercial power supply (hereafter, this situation will be referred to as an input-output misconnection), damaging the ballast. The installer may also unintentionally connect one end (or both ends) of the output terminal to a fixture that is electrically grounded to earth, while the commercial power supply is connected to the input terminals and the high-pressure discharge lamp is connected to the output terminals (hereafter, this situation will be referred to as a ground misconnection), which again, may result in damage to the ballast when the commercial power supply is applied to the incorrectly wired ballast.
The operation of a discharge lamp lighting device when an input-output misconnection occurs with a ballast comprising a buck chopper and polarity reversing combination topology will be described with reference to FIG. 1B of the drawings, which illustrates a portion of a discharge lamp lighting device of the present invention. It is noted that while the following discussion is provided with respect to a discharge lamp lighting device that employs a buck chopper circuit, the analysis is very similar for a full bridge circuit that omits the buck chopper circuit.
When an installer mistakenly connects a commercial power supply 110 to an external output unit 112 and turns ON the external power supply, an AC power supply voltage is applied from the commercial power supply 110 through the external output unit 112 to connection point B associated with switching elements Q3 and Q4, and connection point C associated with switching elements Q5 and Q6. When this occurs, the AC power supply voltage is rectified by a diode bridge formed by diodes D3, D4, D5 and D6, which are parasitic diodes of the switching elements Q3, Q4, Q5 and Q6, respectively. The rectified voltage is applied to capacitor C1 in a DC power supply 102 via inductor L2 and diode D7 (which is a parasitic diode of switching element Q2) of a buck chopper circuit 104, which charges the capacitor C1.
When capacitor C1 is charged, the voltage on capacitor C1 (i.e., a voltage at point A in FIG. 1B) is supplied to control an auxiliary power supply unit 109, which provides electrical power to a DC power supply controller 107 and an inverter controller 108. Upon being supplied with the power supply voltage (electrical power) for operation, the inverter controller 108 starts a switching operation for lighting a high-pressure discharge lamp 113. In other words, the switching elements Q3, Q4, Q5 and Q6 are switched ON and/or OFF, as shown in FIG. 2-1, to alternate the DC voltage output from the buck chopper circuit 104 and to generate a high pulse voltage in conjunction with the igniter circuit in the polarity reversing circuit 105. The high pulse voltage is applied through the external output unit 112 to the high-pressure discharge lamp 113.
Since the AC power supply voltage from the commercial power supply 110 is being applied to the ballast through the external output unit 112 to connection point B of switching elements Q3 and Q4 and connection point C of switching elements Q5 and Q6, when switching element Q4 is switched ON by the inverter controller 108, a current path is formed from connection point C to connection point B through switching element Q4 and diode D6. A shunt current flows from connection point C to connection point B through the commercial power supply 110, which is connected to the external output unit 112. Thus, one or more of the switching element Q4, diode D4, and switching element Q6 (with its parasitic diode D6), may be damaged or destroyed.
Similarly, when switching element Q6 is switched ON by inverter controller 108, a current path is formed from connection point B to connection point C through switching element Q6 and diode D4. A shunt current flows between connection points B and C through the commercial power supply 110, which is connected to the external output unit 112. Thus, one or more of the switching element Q6, diode D6, and switching element Q4 with its parasitic diode D4, may be damaged or destroyed.
Thus, a problem arises. Specifically, when the installer mistakenly connects the commercial power supply 110 to the external output unit 112, the discharge lamp lighting device 101 may fail. It is noted that such a problem is not limited to the above described example. Whenever a power supply voltage is applied to the external output unit 112, the above-described problem may occur with respect to a discharge lamp lighting device having a configuration in which: (a) the auxiliary power supply unit 109 generates a power supply from the commercial power supply 110 for the operation of other circuit blocks; (b) the switching operation starts for an inverter unit 103 to supply an AC voltage to an external output unit 112 as soon as the inverter controller 108 is energized by the auxiliary power supply unit 109; and (c) the impedance looking into the output terminals of the external output unit becomes extremely small because of the switching action of the inverter unit.
The following explains the operation of a discharge lamp lighting device 101 when the ground misconnection occurs in a ballast having the buck chopper and polarity reversing combination topology in which the protector of the present invention (to be discussed below) is not included. It is noted that the following analysis would be similar for a full bridge topology that omits the buck chopper circuit.
When the installer mistakenly connects one end of the commercial power supply 110 to one end (or both ends) of the external output unit 112, directly or indirectly through earth ground, and switches ON the external power supply while the commercial power supply 110 is connected to the external voltage receiving unit 111, an AC power supply voltage is applied from the commercial power supply 110 to connection point B of switching elements Q3 and Q4 and/or to connection point C of switching elements Q5 and Q6. The AC power supply voltage is rectified by bridge DB1, and applied to capacitor C1 (via inductor L1 and diode D1) to charge capacitor C1 to a peak value of the commercial power supply voltage.
When capacitor C1 is charged, the voltage on capacitor C1 (e.g., the voltage at connection point A in FIG. 1B) energizes auxiliary power supply unit 109, which in turn supplies electrical power to the DC power supply controller 107 and the inverter controller 108 for the operation of the DC power supply circuit 102 and the inverter unit 103, respectively. Upon being supplied with electrical power, inverter controller 108 starts the switching operation to light the high-pressure discharge lamp 113, as was described above. In other words, the switching elements Q3, Q4, Q5 and Q6 are switched ON and/or OFF, as shown in FIG. 2-1, to alternate the DC voltage output from the buck chopper circuit and to generate a high pulse voltage in conjunction with the igniter circuit in the polarity reversing circuit 105. The high pulse voltage is applied through the external output unit 112 to the high-pressure discharge lamp 113.
Since one end of the commercial power supply 110 is connected to connection point B of switching elements Q3 and Q4 and/or connection point C of switching elements Q5 and Q6, when switching element Q4 is switched ON by the inverter controller 108, a current path is formed from connection point B to switching element Q4 to bridge DB1 to commercial power supply 110 and back to connection point B. As a result, a very low impedance path is formed, and a shunt current flows through switching element Q4. Thus, switching element Q4 may be damaged or destroyed.
Similarly, when switching element Q6 is switched ON by the inverter controller 108, a low impedance current path is formed from connection point C through switching element Q6. Shunt current flows from connection point C through commercial power supply 110 and back to connection point C, potentially damaging or destroying switching element Q6.
Therefore, when the installer mistakenly connects one end of the commercial power supply 110 to one or both ends of the external output unit 112 directly (or indirectly) through earth ground while the commercial power supply 110 is connected to the external voltage receiving unit 111, the discharge lamp lighting device 101 may be damaged.
It is noted that such a problem is not limited to the above described example. A similar problem may occur with respect to a discharge lamp lighting device 101 that has a configuration in which: (a) the auxiliary power supply unit 109 generates a power supply from a commercial power supply for the operation of other circuit blocks; (b) the switching operation starts for the inverter unit 103 to supply an AC voltage to an external output unit 112 as soon as the inverter controller 108 is energized by the auxiliary power supply 109; and (c) the impedance looking between one end of the input terminal and one or both ends of the output terminal 112 becomes extremely small because of the switching operation of the inverter unit 103.
The present invention addresses the above-described problems. According to a feature of the present invention, the occurrence of a failure due to an input-output misconnection and/or ground misconnection can be avoided or minimized. In the present invention, the auxiliary power supply unit 109 is deliberately energized at an initial start-up, so that the inverter controller 108 is energized. A protector is provided that functions to determine electrical connection characteristics of the discharge lamp lighting device and determine whether the polarity reversing circuit of the discharge lamp lighting device can be safely operated. If the protector determines that the electrical connection characteristics represent a mis-wiring situation, the protector inhibits the operation of the switching elements Q3 to Q6 of the discharge lamp lighting device.
In order to achieve the above-describe objective, a discharge lamp lighting device of the present invention includes an external voltage receiving unit, a DC power supply unit, an inverter unit, an external output unit, a controller and a auxiliary power supply unit. The external voltage receiving unit receives an input voltage from the external power supply. The DC power supply unit generates a regulated DC voltage from the power supply voltage received at the external voltage receiving unit. The inverter unit converts the DC voltage that is generated by the DC power supply unit to a periodic AC voltage to light a high-pressure discharge lamp. The external output unit supplies the AC voltage generated by the inverter unit to the external discharge lamp. The inverter controller controls the operation of the inverter unit. The auxiliary power supply unit that is connected to the output of the DC power supply unit generates the power supply voltage for the operation of the inverter controller.
According to this configuration, if the commercial power supply voltage is applied to the external output unit, the auxiliary power supply unit generates a power supply voltage for the operation of the inverter controller, while the protector functions to protect the discharge lamp lighting device from failure.
Even if one end of the commercial AC power supply is connected to one or both ends of the external output unit, directly or indirectly, through earth ground while the commercial AC power supply voltage is applied to the external voltage receiving unit, the protector will function to protect the discharge lamp lighting device from failure.
The protector comprises a detector, a comparer and an inhibitor. The comparer compares a voltage between at least one point of an internal circuit of the discharge lamp lighting device (or an equivalent value of the voltage), sampled by the detector, with a reference voltage (or an equivalent value of the reference voltage). The inhibitor restricts any switching operation of the polarity reversing circuit based upon the result of the comparison during a period from when the AC power supply voltage is applied to the discharge lamp lighting device (ballast) to when the switching operation starts for the inverter unit to output a voltage to the external output unit.
According to the above, a regulated DC voltage is generated by the DC power supply unit from the power supply voltage received from the external voltage receiving unit. The regulated DC power supply voltage is converted to a periodic AC voltage by the inverter unit. The AC voltage is supplied to the external output unit to energize the discharge lamp. If a power supply voltage is mistakenly applied to the external output unit, or one end of the AC power supply is mistakenly connected to one or both ends of the external output unit, directly or indirectly, through earth ground while it is still connected to the external voltage receiving unit, a voltage between two points of the internal circuit is detected and compared. In response to the comparison, the operation of the inverter unit is selectively prevented. As a result, the formation of a shunt current loop through the power supply and the internal switching elements is prevented, thereby preventing damage to the discharge lamp lighting device (ballast).
According to an object of the present invention, an apparatus is disclosed that protects a discharge lamp lighting device from damage resulting due to mis-wiring of a source of electrical power to the discharge lamp lighting device. The protector comprises a detector that samples at least one monitor point associated with the discharge lamp lighting device to obtain at least one detection voltage, a comparer that compares the at least one detection voltage with a reference voltage, and an inhibitor that inhibits an operation of the discharge lamp lighting device when a result of the comparison indicates that a mis-wiring of the power supply to the discharge lamp lighting device exists.
According to a feature of the invention, the at least one detection voltage is obtained by sampling a voltage at a junction of a switching element associated with a polarity reversing circuit of the discharge lamp lighting device. The inhibitor determines that the mis-wiring exists when the at least one detection voltage is greater than the reference voltage that is less than the square root of 2 (e.g., approximately 1.414) times a commercial power supply.
According to another feature of the invention, the at least one detection voltage is obtained by sampling an output voltage of a DC power supply of the discharge lamp lighting device, and the comparer determines that a mis-wiring of the power supply to the discharge lamp lighting device exists when the sampled output voltage does not exceed the reference voltage. Alternatively, the at least one detection voltage is obtained by sampling an output voltage of a buck chopper of the discharge lamp lighting device, and the comparer determines that a mis-wiring of the power supply to the discharge lamp lighting device exists when the sampled output voltage does not exceed the reference voltage. Still further, the at least one detection voltage may be obtained by sampling an output voltage of a rectifier of the discharge lamp lighting device, with the comparer determining that a mis-wiring of the power supply to the discharge lamp lighting device exists when the sampled output voltage does not exceed the reference voltage.
According to another object of the invention, a method is disclosed for protecting a discharge lamp lighting device from damage due to mis-wiring of a source of electrical power to the discharge lamp lighting device. At least one monitor point associated with the discharge lamp lighting device is detected to obtain at least one detection voltage that is compared with a reference voltage. The operation of the discharge lamp lighting device, such as a switching operation of a polarity reversing circuit, is inhibited when a result of the comparison of the at least one detection voltage with the reference voltage determines that a mis-wiring of the power supply to the discharge lamp lighting device exists.
According to a feature of the invention, an output voltage is detected at a junction of a pair of switching elements of the polarity reversing circuit of the discharge lamp lighting device, a switching operation of the pair of switching elements being inhibited when the comparing of the detected output voltage with the reference voltage indicates that the detected output voltage is greater than the reference voltage.
According to another feature of the invention, the switching operation of the polarity reversing circuit of the discharge lamp lighting device is inhibited when the comparison of the at least one detection voltage with the reference voltage indicates that the at least one detection voltage exceeds the reference voltage.
A still further feature of the invention is that the switching operation of the polarity reversing circuit of the discharge lamp lighting device is inhibited when the comparison of the at least one detection voltage with the reference voltage indicates that the reference voltage exceeds the at least one detection voltage.
According to another object of the invention, an apparatus is disclosed for lighting a discharge lamp. The apparatus includes a DC power supply that generates a predetermined DC voltage in response to an AC power source from an external voltage receiver, a DC power supply controller that controls an operation of a switching element of the DC power supply, an inverter having a plurality of switching elements that changes the predetermined DC voltage to an AC voltage sufficient to light a discharge lamp, an inverter controller that controls an operation of the plurality of switching elements of the inverter, an external outputter that supplies the AC voltage from the inverter to the discharge lamp, an auxiliary power supply that generates an operating voltage to power the DC power supply controller and the inverter controller based upon the power source from an external voltage receiver, the auxiliary power supply being configured to generate the operating voltage to power the inverter controller even if the AC power source is supplied to the external outputter, and a protector that operates to inhibit the operation of the plurality of switching elements of the inverter in response to a comparison of a monitor voltage obtained from the discharge lamp lighting apparatus with a reference voltage.
According to a feature of the invention, the monitor voltage represents a voltage at a junction of a pair of the plurality of switching elements of the inverter, and the protector inhibits the operation of the plurality of switching elements when the monitored voltage is determined to exceed the reference voltage, while enabling the operation of the plurality of switching elements when the monitored voltage is determined to be less than the reference voltage.
According to another feature of the invention, the monitor voltage represents the predetermined DC voltage of the DC power supply, and the protector inhibits the operation of the plurality of switching elements when the predetermined DC voltage is determined to be less than the reference voltage, while enabling the operation of the plurality of switching elements when the DC power supply is determined to be greater than the reference voltage.
According to a variation of the invention, the inverter includes a buck chopper, and the monitor voltage represents an output voltage of the buck chopper. The protector inhibits the operation of the plurality of switching elements when the output voltage of the buck chopper is determined to exceed the reference voltage, while enabling the operation of the plurality of switching elements when the output voltage of the buck chopper is determined to be less than the reference voltage. In this variation, the reference voltage is significantly less than a normal output voltage of the buck chopper.
According to another variation, the inverter includes a buck chopper, with the monitor voltage representing an output voltage of the buck chopper. The protector functions to inhibit the operation of the plurality of switching elements when the output voltage of the buck chopper is determined to be less than the reference voltage, and enables the operation of the plurality of switching elements when the output voltage of the buck chopper is determined to be greater than the reference voltage. In this variation, the reference voltage approximates a normal output voltage of the buck chopper.
In another variation, the DC power supply comprises a boost chopper, with the monitor voltage representing an output voltage of an AC-to-DC voltage converter. The protector inhibits the operation of the plurality of switching elements when the output voltage of the AC-to-DC voltage converter is determined to be less than the reference value, and enables the operation of the plurality of switching elements when the output voltage of the AC-to-DC voltage converter is determined to be greater than the reference value.